New Method to Protect Circuits

Arc-fault circuit-interrupter(AFCI) protection requirements were first submitted to the National Electrical Code (NEC) process for the 1996 NEC but were not accepted until the 1999 NEC. These requirements as detailed in Section 210.12 were expanded for the 2002 NEC and have been changed again for the 2005 NEC.

In the 1999 NEC, AFCI protection was required for 15- and 20-ampere, 125-volt, single-phase branch circuits supplying dwelling-unit bedroom receptacle outlets with an effective date of Jan. 1, 2002. In the 2002 NEC, AFCI protection was expanded to cover all 15- and 20-ampere, 125-volt, single-phase branch circuits supplying dwelling-unit bedroom outlets, including receptacles, luminaires, ceiling fans and other loads. The intent of both the 1999 NEC and the 2002 NEC was to provide AFCI protection for the entire branch circuit, as are the requirements in the 2005 NEC with an exception added. To understand the changes that occurred in the various NEC editions, one must first understand the various types of AFCI devices listed and designed to de-energize the circuit when an arcing fault occurs.

Six different types of AFCI devices are designed to provide protection against parallel arcing, series arcing, or both series and parallel arcing. A series arc is a break in a single conductor where the arcing takes place between the broken conductor ends. A parallel arc is from line-to-line or line-to-ground.

A portable AFCI device is intended to be connected to a receptacle while providing protection for connected cord sets and power-supply cords against unwanted effects of arcing. A similar AFCI device is the cord-type device where the device may be built into the cord or cord cap. These AFCI devices are not designed to protect the entire branch circuit, so they would not be used as the protection method required in accordance with Section 210.12. A listed cord AFCI would be used for a cord-connected air conditioner to comply with Section 440.65.

An outlet circuit AFCI device is one that is to be installed at a branch-circuit outlet as a primary method of protection for cord sets and power-supply cords. These devices may or may not, depending upon design, provide feed-through protection for downstream receptacles. Ultimately, they will provide protection for cord sets and power-supply cords against arcing faults. These devices may or may not have integral receptacles designed into the device.

The outlet branch-circuit AFCI device has been evaluated to provide protection for the downstream branch-circuit wiring, cord sets and power-supply cords. These devices also provide protection to upstream branch-circuit wiring. These devices are designed to be installed as the first outlet in a branch circuit and have feed-through connections for downstream protection of additional outlets. The outlet branch-circuit AFCI device provides no parallel-arc protection upstream but does provide parallel and series (with and without grounding in the branch circuit) arc protection downstream with limited series protection upstream.

The branch/feeder type AFCI device is installed at the origin of the branch circuit or feeder at a panelboard and functions to de-energize the entire branch circuit when an arcing fault is detected. These devices can be self-contained within an enclosure or as part of a circuit breaker. Since this device is located at the origin of the branch circuit or feeder, upstream protection is not an issue, but it will provide parallel-arcing protection and series protection for circuits with ground. It will not provide series-arc protection for circuits that are not grounded and will not provide series-arcing protection for extension-cord sets and power-supply cords.

A combination-type AFCI has been evaluated to provide protection of the branch-circuit wiring, feeder wiring or both, with protection for cord sets and power supply cords connected to receptacles. These devices may be self-contained with an enclosure, separate devices mounted in an enclosure or an outlet box, or integrated into a circuit breaker or receptacle. These devices are designed to detect both series and parallel arcing faults.

The 2005 NEC permits branch/feeder AFCIs to be installed until Jan. 1, 2008, and after that date, all devices installed must then be listed as a combination-type device that will provide protection for the branch circuit at the point of origin. An exception has also been added to permit the location of an AFCI device to be installed within six feet of the branch-circuit overcurrent device, measured along the branch-circuit conductors but only where installed in a metal raceway or a cable with a metal sheath.

These new requirements in the 2005 NEC will provide greater protection plus provide a method to protect circuits in existing buildings where older panels may not have AFCI circuit breakers designed to be installed in them. EC

ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 or at mark.c.ode@us.ul.com.